The vertebrae of the human spine are arranged in a column with one vertebra on top of the next. Between adjacent vertebrae exists an intervertebral disc that transmits force between adjacent vertebrae and provides a cushion between the adjacent vertebrae.
Degeneration or other deformities in the intervertebral disc (the “diseased disc”) can cause back pain. When a diseased disc repeatedly impinges upon neurological structures or is determined to be a pain generator, surgeons conventionally treat the diseased disc by surgically removing the diseased disc and inserting a bone graft or other device in the space vacated by the diseased disc. The adjacent vertebrae are then immobilized relative to one another with stabilization hardware. Eventually, the vertebrae grow into one solid piece of bone.
While fusing the vertebrae into one solid piece of bone is the conventional practice, fusing adjacent vertebrae into a single bone mass is a less than ideal solution. In particular, fusing two or more vertebrae into a single bone mass causes additional stress on the remaining vertebrae and discs accelerating any potential degeneration. Moreover, the fused bone mass may lead to decreased motion and flexibility in the spine. The decreased motion and/or flexibility is exacerbated when three or more vertebrae are fused.
In order to avoid fusing two or more vertebrae into a single bone mass, prosthetic devices have been developed that attempt to mimic the intervertebral disc, both size and function. The prosthetic device is implanted into the intervertebral space to replace the diseased disc. U.S. Pat. No. 5,458,642, titled SYNTHETIC INTERVERTEBRAL DISC, issued Oct. 17, 1995, to Beer et al. discloses one such prosthetic device. The Beer et al. device includes a plurality of coiled springs interspersed between two endplates. The springs of the Beer et al. device attempt to approximate the function of the replaced intervertebral disc. The Beer et al. device is less than satisfactory because the coiled springs can be damaged and lose their elasticity over time. Further, the coiled springs provide limited shock absorption requiring the use of a compressible pouch of biocompatible material to provide additional shock absorption. Moreover, adjacent vertebrae need significant separation to allow for insertion of the prosthetic device potentially causing trauma to the surrounding structures.
U.S. Pat. No. 5,676,702, titled ELASTIC DISCPROSTHESIS, issued Oct. 14, 1997, to Ratron, provides another device that attempts to mimic the replaced intervertebral disc. The Ratron device includes the same endplates separated by an elastic post and elastically deformable partitions. The Ratron device is relatively impractical, however, because the placement of the elastic post and the elastically deformable partitions is difficult and varies on a case-by-case basis. Thus, manufacturing the device prior to surgical implantation is difficult. Further, bone or other tissue growth into the intervertebral space can foul the device making it inoperable. Moreover, adjacent vertebrae need significant separation to allow for insertion of the prosthetic device potentially causing trauma to the surrounding structures. Finally, similar to springs, the elastic material may experience plastic deformation causing failure of the prosthesis. Additionally, the elastic material contained in the Ratron device may degrade over time.
While many artificial intervertebral discs exist, all of them use either coiled springs or plastics to approximate the function of the removed disc. As shown above, these artificial discs suffer many drawbacks. Thus, it would be desirous to develop an improved artificial intervertebral disc.